The present Application claims priority from Korean Patent Application Number 10-2002-0040101 filed in the Republic of Korea on Jul. 19, 2002, which Korean application is incorporated in full herein by reference.
1. Field of the Invention
The present invention generally relates to a color separating device and an image projecting apparatus using the same, and more particularly, it relates to a color separating device using a dichroic mirror wheel capable of minimizing light loss by using a plurality of dichroic mirror wheels, and an image projecting apparatus using the color separating device.
2. Description of the Related Art
Apparatuses like projectors and projection systems display a predetermined image on a screen by projecting a light generated at a light source onto the screen through an optical system. Such displays are used in many places, namely, in meetings for presentation, and in theaters and homes.
Recently, optical devices such as projectors or projection systems have usually been provided with a digital micromirror device (DMD), providing far clearer images than do liquid crystal displays (LCD) or cathode ray tubes (CRT).
The DMD has a number of micromirrors corresponding to the given resolution. The micromirrors control light reflection in accordance with the input signals. Briefly put, the DMD is a semiconductor optical switch using a set of micro-mirrors. Since the DMD seldom has light loss, it has an excellent color representation and brightness.
FIG. 1 is a view showing the basic structure of a conventional image projection apparatus using a color filter wheel.
Referring to FIG. 1, the conventional image projection apparatus 100 using the color filter wheel includes a light source 110, a color filter wheel 120, a light tube 130, a lens 140, a DMD panel 150 and a projection lens 160. The one-dotted line in FIG. 1 represents an optic path of white light.
The light source 110 emits a white light, and can be an arc lamp or a laser. The color wheel 120 is rotated in the arrowed direction by a rotating means (not shown), and divided into a red (R), green (G) and blue (B) divisions. The white light emitted from the light source 110 is transmitted through the R, G and B divisions and split into rays of light, i.e., R, G and B beams.
The light tube 130 is formed as a hollow hexahedron having a through hole penetrating therein. The R, G and B beams from the color wheel 120 are transformed into a square beam inside of the light tube 130. The square beam of the laser beam is dispersed at the lens 140 to be incident on the DMD panel 150.
The DMD panel 150 includes a plurality of micromirrors 150a. The R, G and B beams of respective wavelength form corresponding monochromatic color stripes on the DMD panel 150 by order of incidence, and are reflected from the micromirrors 150a of the DMD panel 150. The reflected R, G and B beams transmit through the projection lens 160 and form an image on the screen.
The image projection apparatus 100 described above can fast-process in response to the split R, G and B beams by the independently-driven micromirrors 150a. In other words, good quality color image can be obtained with simple structure. However, in the case of using a color filter, only a third of the light quantity from the light source is incident on the DMD panel 150.
This is because 60-70% of the white light emitted from the light source is blocked at the color wheel 120. While the R beam is evenly projected on the entire panel, other beams, i.e., G and B are completely blocked by the color filter and discarded. The same situation also applies with respect to the G and B beams. Accordingly, since only a third of the incident white light is utilized according to the color filter method, the light utilization decreases.